GRAL

GRAL, the Graz Lagrangian Model, is a dispersion model developed since 1999 at the Institute of Thermodynamics and Sustainable Propulsion Systems at Graz University of Technology. With its companion wind-field model GRAMM it forms the GRAMM/GRAL system, which the institute says is used both in research and in regulatory assessments of urban air quality. It was first built for the frequent low-wind conditions of inner-Alpine basins in Austria, where wind is below 1.5 m/s for up to 90 per cent of the time, and it handles dispersion across the full range of wind speeds and stability conditions.

It simulates chemically non-reactive pollutants in built-up areas and complex terrain, with a micro-scale flow model that accounts for buildings and building downwash; stack emissions with temperature and exit velocity; dispersion from road tunnel portals, meeting the Austrian guideline RVS 04.02.12; dry and wet deposition and sedimentation; decay such as bacteria die-off; and flow within vegetation layers. For smell it computes odour hours from a concentration-variance model. Runs can be steady-state or transient, for instance for puff releases.

The model system is freeware. It is downloaded from the TU Graz site after registering with some basic details; the download page gives no warranty of completeness or correctness and puts the risk of correct application on the user. The pages read do not name a source licence or a public repository. The institute offers trainings.

Status: in use; the download site was renewed in November 2022, and the home page gives no later date.